Barrier membranes and inflatable bladders formed from such membranes have been used in footwear. It is often desirable to use thermoplastic polymeric materials to form the membranes because thermoplastic materials may be reclaimed and reformed into new articles, reducing waste during manufacturing operations and promoting recycling of scrap. Barrier membranes for inflated bladders can thus be made with a thermoplastic barrier layer. Thermoplastic polymeric barrier layer materials typically form crystalline regions or spherulites that serve to make the egress of fluid molecules through the layer more difficult.
Thermoplastic polymeric barrier materials with at a thickness adequate to provide the desired low gas transmission rate [GTR] generally do not have a low enough modulus for cushioning in shoes because the inflated bladder is subjected to high strains during use. In order to overcome this problem, the barrier materials have been blended or layered with elastic materials. Elastic materials, or elastomers, are able to substantially recover their original shape and size after removal of a deforming force, even when the part has undergone significant deformation. Elastomers may likewise be thermoplastic, and so a flexible, thermoplastic barrier film may be formed with a combination of thermoplastic elastomers and thermoplastic barrier layer materials.
In footwear, styling considerations have made low haze, transparent barrier membranes desirable. A blend material may be cloudy or hazy, however, if the materials blended together in a layer are not entirely compatible. A related problem arises in recycling scrap membrane material. When a membrane has been constructed with layers of different materials, those materials are not easily separated in the scrap. Consequently, the multi-layer scrap must be blended into one or another of the layer materials for recycling. For the desired clarity to be preserved in the blended layer, the multi-layer scrap material must be compatible with the layer material into which it is blended.
One type of thermoplastic elastomer that has been blended or layered with the barrier materials to make resilient membranes is thermoplastic polyurethane. Membranes including a first layer of a thermoplastic polyurethane, and a second layer including a barrier material, such as a copolymer of ethylene and vinyl alcohol, are described, for example, in U.S. Pat. No. 6,082,025, issued Jul. 4, 2000; U.S. Pat. No. 6,013,340, issued Jan. 11, 2000; U.S. Pat. No. 5,952,065, issued Sep. 14, 1999; and U.S. Pat. No. 5,713,141, issued Feb. 3, 1998, each of which is incorporated herein by reference. Although membranes with separate layers of the thermoplastic polyurethane material and the polymeric barrier material have had acceptable clarity, recycling scrap multi-layer membrane material by blending the scrap material into one of the layers has been problematic. In particular, the blended layer and membrane have noticeably lower reduced clarity because of incompatibility of the blended materials.
Thus, it would be desirable to have a transparent, multi-layer membrane in which the layer compositions are compatible so that incorporation of the multi-layer scrap into one layer of the membrane does not result in undesirable haziness.